Alloy



-multitude of galvanic couples.

Patented June 30, 1942 ALLOY Louis Henri Francois Canac andEmilc AugusteMarie Antoine Segol, Toulon, France No Drawing. Application June 19,1939, Serial No. 279,992 In France July 11, 1936 4 Claims.

Our invention relates to light and ultra-light alloys containingaluminum and magnesium. More particularly it relates toaluminum-magnesium base alloys and a method of making the same wherebycertain desirable properties in I such alloys are assured. Thisapplication is a continuation-in-part of our application Serial No.150,880, filed June 28, 1937.

The principal object of the invention resides in the provision of aself-protecting filmcn the surface of thealloy which guards the alloyfrom corrosion in sea water and the like. This film has the remarkablecapacity of cicatrizing. That is, if the film is fractured or broken,this fracture is immediately closed up or healed by the automaticformation of a protective scar.

Ordinary aluminum magnesium base alloys heretofore known do not possessthis remarkable property. While some of the literature has givenexamples of aluminum-magnesium base alloys which are resistant tocorrosion, no example has been disclosed of an alloy having aself-healing protective film, and no disclosure, of which we are aware,has in any way taught how an alloy having such a remarkable property canbe produced particularly with any degree of assurance.

The invention is based on a remarkable discovery we have made after manyexperiments and is based on a new principle.

According to this new principle and discovery, an alloy is formed ofaluminum and magnesium, and by utilizing predetermined proportions ofthese base metals, and by adding one or more other metals which meetvery. rigid requirements as to amounts and properties, there isautomatically formed on the surface of the alloy a uniform, adherentleak-proof, protective film which possesses the astounding property ofcicatrizing (forming a scar, healing, closing up) immediately afterfracture.

It is consequently the principal object of our invention to provide suchanalloy and a method whereby it may be produced, not haphazardly andperchance occasionally, but every time the dictates of the followingspecification are followed.

A more specific object of the invention is the provision of an alloyhaving a self-protective and self-healing film and having a finelyheterogeneous, approximately eutectic structure which, when certainrequisites of the invention are carried out, results in the formation ofa These galvanic couples, being finely distributed, assure the rapidformation of the protective film in the presence of a normally corrosiveagent such as sea water.

As already indicated the results desired can only be obtained by rigidlyobserving certain requisites. Particularly these requisites will now bedescribed.

The alloyhas a base of aluminum and mat,- nesium. These base metalsshould be employed only in an extremely pure state. Impurities should beavoided and in any case should be less than 0.10%. This is particularlyso of iron and silicon whose presence is exceptionally undesirable andeven fatal to the results desired.

When the base of the alloy is such that aluminum predominates, then theproportion of magnesium present should under no circumstances be lessthan 10%. This percentage is the critical low percentage for magnesium.The many experiments carried out in making the invention demonstratedthat the important results relative to the self-healing film'and themechanical properties of the alloy do not begin to manifest themselvesexcept when the percentage of magnesium used is 10% or greater. Theresults efiected by the invention are increasingly manifest when theproportion of magnesium is greater than 10%.

Moreover, these results are obtained with proportions of magnesiumgreater than 50%. The invention thus extends to the so called ultralightalloys in which magnesium predominates.

The lower and upper limits for aluminum are respectively 1% and An alloycontaining only aluminum and magnesium even with the proportions givenabove will not give the results of the present invention. In addition tothese metals, in the proportions set forth, we have found that theinvention can only be carried out by carefully selecting and adding anadditional metal or metals in accordance with specific requirements.

The additional metal must first of all be easily oxidizable.

Secondly, the additional metal should be more precious than the basemetals. Any other. metal not responding to these conditions should beex.- cluded as an impurity inconsistent with the object desired.

The oxidizing property of the addition metal acts primarily in theelectrolytic formation of unattackable oxides or oxychlorides, whichmake up the protective self-healing film. This, however, is onlyproduced by galvanic couples formed between the addition metal and thebase metals and in which the ions are displaced from the particles ofthe addition metal by the base metal. Hence, the requirement that theaddition metal should be more precious than the base metals aluminum andmagnesium.

When mention is made herein of metals which are more precious than thebase metals, reference is had to the electromotive series which liststhe metals with respect to their activity, that is, the ease with whichthey give up electrons. In general, as is well known, each metaldisplaces the ions of those which follow it in the list.

Another requirement of the addition metal is that it must be capable offorming a eutectic with at least one of the base metals and should bepresent in an amount which preferably will ap-- proximate the amountwhich will form a eutectic with the base metals. This contributes toassure a fine distribution of the metals and gives rise to a greatnumber of elementary piles between which eletrolytic action is exertedto a maximum when the alloy is exposed to the action of a corrosiveagent such as salt water.

The term eutectic is a definite term known to those skilled inmetallurgy. The kinds of metals and the amounts thereof which will forma eutectic with another metal can, of course, be determined from phasediagrams in the technical literature.

When we say that the addition metal should be capable of forming aeutectic mixture with at least one of the basic constituents aluminumand magnesium, and that such addition metal should be present in anamount approximating the amount required to form a eutectic mixture, weintend to cover slight variations. We have found thatv if the additionmetal is present in amounts within -30 to +30 of the eutectic amountsatisfactory results can be obtained.

Any metals which do not meet these requirements are to be excluded, andinsofar as this; invention is concerned such other metals should beregarded as impurities.

While there are several metals which meet the requirements for theaddition metal given above and which can be used in accordance with theinvention, we prefer zirconium as the addition. metal. Insofar aszirconium is concerned this should be added in amounts ranging from 0.05to 0.2% to obtain the best results although amounts up to 2%-may be usedwith the desired results. The lower and upper limits for zirconium. arerespectively 0.01% and,3%.

As specific examples of the invention, a satisfactory alloy can be madewith:

Magnesium 10 Zirconium 0.2

Aluminum Remainder Our preferred example is as follows:

. Per cent Magnesium 11 Zirconium 0.18

Aluminum Remainder approximate values of the proportion correspond- 75Per cent ing to the eutectic of the binary diagram of aluminum and theaddition metals:

Per cent Antimony 1.1 Chromium 0.40-0.77 Cobalt 1 Beryllium 0.90Manganese 1.95 Iitanium 0.15 Cadmium 5 In our alloys containingaluminum, magnesium and zirconium, the effect of the zirconium in thealloy may be augmented by the use of a fourth metal. As an example wemay have an alloy meeting the requirements of the invention and whichconsists of:

Per cent Magnesium 10 Zirconium -4 .2 Titanium 1 Aluminum Remainder Apreferred example using titanium is as follows:

Aluminum Remainder An alloy of the composition just recited showed verygood results when subjected to the action of a corrosive agent. Afteralternate immersion and emersion at thirty minute intervals in sea waterfor two months, no appreciable corrosion was observed. Another sample ofthe same alloy showed no appreciable signs of corrosion after two monthscontinuous immersion.

In all instances the surface of the alloy at the end of the period wascovered with protective film. It was found that the protectiveself-healing film formed more rapidly where the immersionwas continuous.

Mechanical properties of the alloy were found to be particularly goodwhen the alloy is rolled. A breaking strength of 45 kg. and anelongation of the order 17% were obtained. These results are furtherimproved in alloys according to the invention where the proportion ofmagnesium is about 10.5%.

The titanium may be replaced by other metals provided the conditionsreferred to above are carried out. The following metals, for exam ple,may be used if proportions preferably approximate the eutecticproportions, as indicated below, are observed:

Percent Cr 1 Be 2 Mn 3 C0 2 Sb 5 Ni 5 Cd 5 Use may also be made of thefollowing as the fourth metal, in proportions preferably less than BoronBismuth Molybdenum We have found that alloys produced according to theinvention may be further improved by heat treatment, notably tempering.This heat treatment is designed also to improve the fineness ofprecipitation of the crystals formed by the addition metals as well asthe so called beta crystals 5(AlaMgz) The temperature and duration ofthe heat treatment depend both on the percentage of ad-- ditions and themagnesiumcontent of the alloy.

The tempering is not carried to as great a degree where the alloy has ahigh magnesium content, but, in each case, the duration and temperaturethereof have an optimum value. It is particularly important that theduration and temperature should not be carried to coalescence of theprecipitated granules.

By way of example, considering the following example:

Percent Magnesium 11.5 Zirconium 0.18 Aluminium Remainder The heattreatment for giving resistance to.

corrosion is then carried out at a temperature ranging from 245 to 3200., preferably close to this last mentioned value. If it is advisable toeffect a supplementary rolling operation, a new treatment is carried outat a temperature of 400 or more.v In a general manner, for the alloyswith which the invention is concerned the tempering should be used ifthe ingot or rolled plates have been very rapidly cooled. The desiredstructure of the alloy may also be obtained directly by suitable slowcooling of the ingot or of the sheets during the rolling, for example,by

stopping for about fifteen minutes starting from a temperature generallyabove 300 C., in which the granules can precipitate.

We claim: 7

l. A corrosion resistive alloy having a surface formed of a multiple ofgalvanic couples which surface when subjected to corrosive influences iscapable of forming a self-protective, cicatrizing, film, said alloyconsisting of magnesium in the amount of 10%, zirconium in the amount of2%, and the balance being aluminum, said alloy containing less than 0.1%of impurities, all metals being considered as impurities which are noteasily oxidized, are less precious than aluminum or magnesium and whichare incapable of forming a eutectic with aluminum or magnesium.

2. A corrosion resistive alloy having a surface formed of a multitude ofgalvanic couples which surface when subjected to corrosive influences iscapable of forming a self-protective, cicatrizing, film, said alloyconsisting of magnesium in an amount ranging from 10 to 15%, zirconiumin an amount ranging from .05 to 2%, and the balance being aluminum,said alloy containing less than 0.1% of impurities, all metals beingconsidered as impurities which are not easily oxidized, are lessprecious than aluminum or magnesium and which are incapable of forming aeutectic with aluminum or magnesium.

3. A corrosion resistive alloy having a surface formed of a multitude ofgalvanic couples which surface when subjected to corrosive influences iscapable of forming a self-protective, cicatrizing, film, said alloyconsisting of magnesium in an amount ranging from 10 to 50%, zirconiumin an amount ranging from .05 to 2%, and the balance being aluminum,said alloy containing less than 0.1% of impurities, all metals beingconsidered as impurities which are not easily oxidized, are lessprecious than aluminum or magnesium and which are incapable of forming aeutectic with aluminum or magnesium.

4 A corrosion resistive alloy having a surface formed of a multitude ofgalvanic couples which surface when subjected to corrosive influences iscapable of forming a. self-protective, cicatrizing, film, said alloyconsisting of magnesium in the amount of 11%, zirconium in the amount of0.18%, and the balance being aluminum.

LOUIS HENRI FRANCOIS CANAC. EMILE AUGUSTE MARIE ANTOINE SEGOL.

